Numerical simulation of laser-tungsten inert arc deep penetration welding between WC-Co cemented carbide and invar alloys

In order to optimize the laser-tungsten inert arc (TIG) welding process of cemented carbide to steel, a novel combined model consisting of circular disk source, line source, and double ellipsoidal TIG heat source was put forward to simulate the deep penetration phenomena and bead profile. In contrast, laser heat source model was validated using macrostructure analysis results. The effects of the circular disk of radius and the material properties on the bead profile were discussed. For mechanism surface formation, surface depression or humps was discussed based on the high-speed photography technique to verify bead profile characterization. The results manifested that in the model, the circular disk radius played a key role in the formation of bead profile. And the penetration coefficient chiefly affected the root of weld and the keyhole formation. During the hybrid welding, the main forces influencing the surface depression or humping were intrinsic stress from coefficient of thermal expansion gradient, surface tension, buoyancy force, stirring action, and shock waves at the end of the keyhole. Before the solidification of the upper part of the melt, the melt was driven by the fluctuated plasma, plumes, or other forces. While the amount of melt filling the back welds metal of keyhole was larger than that caused by plume losses and the shrinkage of weld metal, the humps came into being.